The invention relates to a disc brake having a brake caliper in which there are arranged two brake pads which, in their function, can be pressed against a brake disc. An action-side brake pad can be actuated by way of a brake-application device via at least one brake plunger. The brake plunger is guided through an opening of a closure cover which closes off a receiving chamber of the brake caliper, wherein, to seal off the receiving chamber, a corrugated bellows bears against the brake plunger and, at the other side, against the closure cover.
In order for functionally relevant components arranged in a receiving chamber of the brake caliper to be protected against corrosion owing to weather influences, an installation opening of the receiving chamber on the side assigned to the brake-application-side brake pad in the case of a sliding-caliper brake is substantially closed off by way of a closure cover.
In this case, the closure cover has openings through which brake plungers are guided, which brake plungers are pressed against the brake pad via the brake-application device during a braking operation. This functional principle is realized both in the case of a disc brake with one central brake plunger and also in the case of a disc brake with multiple, preferably two, brake plungers arranged parallel to and spaced apart from one another. For simplicity, the variant with one brake plunger will be described below.
To seal off the passage region of the brake plunger, a corrugated bellows is provided. The corrugated bellows bears sealingly at one side against the brake plunger and is fastened at the other side to the closure cover, in this case conventionally to a collar which delimits the passage opening at the boundary and which is oriented axially parallel to the brake plunger.
Furthermore, as a redundant seal element, a so-called secondary seal is provided. The secondary seal is arranged behind the corrugated bellows in the direction of the receiving chamber and, by which, the receiving chamber is protected against coarse dirt in the event of a possible failure of the corrugated bellows.
The secondary seal, which is arranged concentrically with respect to the corrugated bellows, bears firmly against the brake plunger and is held in positively locking fashion on the collar of the closure cover. For this purpose, in known constructions, corresponding recesses are provided on the collar, said recesses being engaged into by retention devices, adapted to said recesses, of the secondary seal.
However, the recesses, which are often of bead-like form, of the collar can be produced only with considerable outlay in terms of manufacturing. This is because in the case of the closure cover composed of sheet metal, they are normally formed by punching. This relatively complex bead contour opposes simple and inexpensive production, which also includes the provision of correspondingly complex tooling.
During a brake application process, the brake plunger is displaced axially, such that the secondary seal which bears firmly against it, and which, as mentioned, is held at the other side on the positionally fixed closure cover, is correspondingly deformed. To permit said deformation without damage, the secondary seal must be equipped with a so-called compensation fold, which is possible only with correspondingly high manufacturing outlay, which opposes an optimization of production costs.
Furthermore, the corrugated bellows, on the one hand, and the secondary seal, on the other hand, form an interior space. For necessary pressure equalization of said interior space with respect to the surroundings, an opening must be provided either in the secondary seal or in the corrugated bellows. The formation of the opening likewise requires high manufacturing outlay, including corresponding tooling costs. All in all, the known seal arrangement is an unsatisfactory solution for the sealing of the receiving chamber.
The invention is based on the object of further developing a disc brake of the above-mentioned type such that the secondary seal can be produced more easily and thus at lower cost, and its functional reliability can be improved.
This and other objects are achieved by a disc brake having a brake caliper in which there are arranged two brake pads which, in their function, can be pressed against a brake disc. An action-side brake pad can be actuated by way of a brake-application device via at least one brake plunger. The brake plunger is guided through an opening of a closure cover which closes off a receiving chamber of the brake caliper, wherein, to seal off the receiving chamber, a corrugated bellows bears against the brake plunger and, at the other side, against the closure cover. On the closure cover is also held a secondary seal which is arranged concentrically with respect to the corrugated bellows and which bears slidingly against the brake plunger.
By virtue of the fact that, according to the invention, the secondary seal bears slidingly against the brake plunger, the flexing described with regard to the prior art no longer occurs, which, firstly, significantly minimizes the loading of the secondary seal and, secondly, makes it possible for the secondary seal to be produced significantly more easily, in particular because the described compensation fold can be dispensed with.
In this case, the secondary seal may be composed of a rigid carrier element, for example of a sheet-metal part produced by simple deformation, into which sealing material is embedded at a corresponding location.
This sealing material performs its function even in small quantities, which, like the described simple manufacture of the carrier element, results in a reduction in production costs. As a sealing material, it is contemplated to use a commercially available, standardized O-ring, which bears against the brake plunger.
According to a further aspect of the invention, provision is made for the secondary seal to be held under spring loading against the closure cover, which may be in the form of a plate. For this purpose, for example, a helical spring may be provided which surrounds the brake plunger and which bears with one end side against the secondary seal, specifically against the support element, and with its other end side against a component connected to the brake plunger.
The compression spring may serve not only for the pressure exertion function of the secondary seal but also for the restoring movement of the brake plunger during intervals between braking operations, and, if appropriate, also for the return movement of the connected brake pad if the latter is connected in an axially secured fashion to the brake plunger.
Although it is the case here, too, that an interior space forms between the corrugated bellows and the secondary seal, pressure equalization is however achieved by virtue of the carrier element bearing indirectly, that is to say without a seal and thus not in an air-tight fashion, against the closure cover.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.